Optimization of Bacillus amyloliquefaciens Lx-11 suspoemulsion by response surface methodology to control rice bacterial blight.

Bacillus amyloliquefaciens Lx-11 can effectively control rice bacterial blight. This study developed a new formulation of B. amyloliquefaciens to further improve its field utilization. This formulation was derived from a raw fermentation broth of B. amyloliquefaciens Lx-11, adsorbed by nano-level fume silica, and emulsified to prepare an oil-in-water B. amyloliquefaciens suspoemulsion (SE). Inert ingredients, including soybean oil, emulsifier ST (a mixture of Span 80 and Tween 80), ethylene glycol, AEC-9NA, and SY-6535 showed good biocompatibility with B. amyloliquefaciens strain Lx-11. A Plackett–Burman experiment demonstrated that sodium alginate, AEC-9NA, and glycol were significant factors affecting the count of viable B. amyloliquefaciens. In addition, results of the steepest ascent experiment showed that concentrations of the three significant factors influencing viability were 1.00 g l⁻¹ for sodium alginate, 15.00 ml l⁻¹ for AEC-9NA, and 20.00 ml l⁻¹ for glycol. A Box-Behnken design was applied to describe the nature of the response surface in the experimental region, and the optimal formulation was determined as follows: 10% silica, 40% soybean oil, 8% ST, 1.51% AEC-9NA, 2.36% glycol, 0.08% sodium alginate, and 2% SY-6535. Under optimized conditions, the viable count of B. amyloliquefaciens Lx-11 SE was up to 9.3×10⁸ colony forming units (cfu) per ml. The results showed that the regression equation model had satisfactory accuracy in predicting the viable count of B. amyloliquefaciens Lx-11 SE. Pot experiments indicated that spraying 200 ml 667 m⁻²B. amyloliquefaciens Lx-11 SE effectively controlled rice bacterial blight with a control effect of 64.8–66.0%, equivalent to 20% Thiosen copper. [ABSTRACT FROM AUTHOR]